In recent years, services that provide applications on the Internet have rapidly become widespread. As one example of this type of service, the SNS (Social Network Service) provides applications such as games for members, who are site users. The SNS manages membership information that identifies the members. The same user has different user information (hereafter called an account) in different applications. The SNS associates these accounts with the membership information so as to be able to provide connected services related to a plurality of applications. In the connected services, users who know each other can recognize which applications they use. (See Patent Document 1, for example.)
In applications such as games, there is a case in which users establish a companion relationship and cooperate with each other to proceed in the game. In an application system that provides connected services, there is a case in which a user invites another user to a game being used by the user.